1. Field of the Invention
The present invention relates to a check valve for allowing a liquid to flow only in one direction. The present invention particularly relates to a check valve for allowing a liquid which is used in a fuel cell to flow only in one direction.
2. Description of Related Art
In a fuel cell which is used in a fuel cell vehicle or the like, an anode is provided on one side of a solid polymer electrolyte membrane and a cathode is provided on the other side of the solid polymer electrolyte membrane, a fuel gas such as a hydrogen gas is supplied to the anode, and an oxidizer gas such as an oxygen or air is supplied to the cathode; thus, a chemical energy which is generated in the oxidation and reduction reaction by these gases is extracted an electric energy directly. In such a fuel cell, a hydrogen gas is ionized in the anode so as to be transferred through the solid polymer electrolyte, and electrons are transferred to the cathode via external load; thus, it is possible to extract electric energy due to an electrochemical reaction in which hydrogen gas and oxygen react to generate water continuously.
Also, in general, in a fuel cell system using such a fuel cell, non-reacted fuel gas is included in a fuel offgas which is exhausted from the fuel cell after the fuel gas is used for generating electricity. Therefore, for the purpose for improving fuel efficiency, the fuel offgas is collected so as to be introduced to a fuel gas supplying path via a fuel offgas circulation path. Thus, the fuel offgas is mixed with fresh fuel gas so as to be supplied to the fuel cell again.
Furthermore, in such a fuel cell system, there are cases in which a highly humid fuel gas remaining in the fuel cell and the fuel gas flow path is scavenged by flowing a low humidity fuel gas by the same path as the case in which the system is operated which does not pass through the fuel cell when an operation of the system is stopped so as to obtain a low humidity atmosphere in the fuel cell and the fuel gas flow path. In such a fuel cell system, check valves are disposed in the fuel offgas circulation path such that a short path such as reverse flow of the low humidity fuel gas in the fuel offgas circulation path does not occur.
Check valves are used not only for such a case but also for any cases in which a flow of a liquid which is used for the fuel cell must be regulated in one direction in the fuel cell system. For such check valves, a reed valve is commonly used because of its simple structure for handling and its cost advantages.
When the reed valve is used in the fuel cell system, the the reed valve must be operable even in the case in which water remaining in the flow path freezes when the fuel cell system is exposed to a below-freezing-point atmosphere. That is, when the reed valve becomes less operable because the water is frozen to stick to movable members, the supply of the fuel gas to the fuel cell is delayed, and smooth startup of the fuel cell is hindered.
In order to avoid such situations, conventionally, contacting surfaces between the reed valve and a valve seat are coated by a an inert member such as tetrafluoroethylene so that the frozen water in unlikely to adhere thereat. In another approach, the reed valves are disposed vertically so that the water which adheres to the reed valve may fall easily.
However, by such conventional approaches to deal with a frozen water in the reed valve, it was not possible to avoid the case in which a little amounts of frozen water remaining in the reed valve are frozen. Therefore, there was a problem in that such a small amount of frozen water increased the load for opening the valve; thus, the operability of the reed valve was deteriorated. Also, in a reed valve which is provided with a stopper for limiting an opening stroke of the valve, it was possible to open the valve even if the water was frozen. However, the opening stroke of the reed valve became narrow due to icy pieces which were generated between the reed valve and the stopper; thus, there was a problem in that the liquid flow was reduced in comparison with the case in which the water is not frozen.